Field of the Invention
The present invention relates to a plugged honeycomb structure, and more particularly, it relates to a plugged honeycomb structure which can inhibit a temperature rise during use at high temperatures and is excellent in thermal shock resistance.
Background Art
An exhaust gas discharged from an internal combustion engine such as a diesel engine, each type of combustion device or the like includes a large amount of particulate matter (hereinafter also referred to as “PM”) mainly composed of soot. When this PM is discharged as it is into the air atmosphere, an environmental pollution is caused. Therefore, in an exhaust system for the exhaust gas, a particulate filter to trap the PM is mounted. An example of the particulate filter is a diesel particulate filter (DPF) for use in purification of the exhaust gas discharged from the diesel engine.
In such a DPF, there is used, for example, a honeycomb structure having porous partition walls defining a plurality of cells which become through channels for the exhaust gas. In this honeycomb structure, plugging portions to plug open ends of cells are disposed in the open ends of the predetermined cells in an end face on an outflow side of the fluid and the open ends of the residual cells in an end face on an inflow side of the fluid, and hence this honeycomb structure is utilized as a plugged honeycomb structure. Hereinafter, a particulate filter such as the DPF in which the plugged honeycomb structure is used will generically be referred to as a “honeycomb filter” sometimes.
As the honeycomb structure for use in the DPF or the like, for example, a ceramic honeycomb structure has been suggested in which partition walls are constituted of main crystals of aluminum titanate in which MgO and SiO2 are solid-dissolved (e.g., see Patent Document 1). Furthermore, as the honeycomb structure, for example, there has been suggested a ceramic structure which has a first phase including β-eucryptite and a second phase including a positive component having higher thermal expansion than a component of thermal expansion of the first phase and which is characterized by microcracks (e.g., see Patent Document 2). In addition, as the honeycomb structure, for example, another honeycomb structure has been suggested in which a heat capacity C represented by a product of specific heat c (kJ/kg·K) and a specific gravity ρ (kg/m3) is from 400.0 to 2000.0 (kJ/m3·K) and a thermal conductivity κ is from 1.0 to 30.0 (W/m·K) (e.g., see Patent Document 3).
In a honeycomb filter such as the DPF, a pressure loss gradually increases due to the PM deposited in the filter with an elapse of time, and hence the PM deposited in the honeycomb filter is periodically burnt and removed to regenerate the filter sometimes. For example, as a method of regenerating the DPF, a regenerating method is known in which a temperature of the exhaust gas discharged from the engine is raised to heat the DPF by using the exhaust gas at the high temperature. An example of a method of raising the temperature of the exhaust gas is a method in which by post jetting to temporarily excessively jet a fuel in a latter half of an explosion stroke or in an exhaust stroke, the excessive fuel is burnt to raise the temperature of the exhaust gas.
[Patent Document 1] WO 2009/63997
[Patent Document 2] JP-A-2004-510676
[Patent Document 3] JP-A-2008-136981